1. Field of the Invention
This invention relates to an electrolytic coating cell for the purpose of forming a coating in the form of a longitudinal track on a band of metal substrate intended for connection to the negative pole of a source of current, comprising a plating head having the form of an elongated prismatic body, a longitudinal portion at least of said prismatic body being formed of a metal section intended for connection to the positive pole of the source of current, the outer surface of said metal section being covered with a layer of impregnable material, a series of ducts distributed along the prismatic body and opening near the layer of absorbent material, an electrolyte supply source, an electrolyte supply circuit, a supply circuit for said series of ducts, a pump for circulating the pressurized electrolyte from the source through the supply circuit, means for bringing said metal substrate into contact with a longitudinal portion of the layer of absorbent material covering said metal section and means for producing longitudinal movement between said head and said substrate in order to form said longitudinal track.
2. Related Art
There are known electrolytic plating cells of this type for electroplating a predetermined area of a plurality of metal pieces arranged side by side to form an electrically continuous band. Such a band may be produced, for example, by stamping and cutting a strip of metal so as to form a succession of distinct laminated pieces transversal to the strip, in particular electrical connectors, attached to a marginal area of the strip and intended for subsequent removal in order to separate the distinct pieces.
Given the fact that one reason for electroplating the contact area of the connectors is to give said area greater resistance to corrosion and ageing, precious metals are preferably used, in particular gold, silver or palladium and their alloys with common metals. Owing to the high price of such metals, an effort is made to limit the extent of the plated area to the active portion of the connectors.
For example, there are plating cells in which a metal substrate is circulated continuously in the form of a band connected to the negative potential of a source of current to form the cathode, while a portion of the substrate's surface is placed in contact with the surface of a flexible, porous material impregnated with an electrolytic solution in contact with an anode. During the course of said movement, the portion of the substrate in contact with the electrolytic solution is covered with an electroplated coating whose thickness depends on the length of contact time and the electrolysis parameters, in particular the composition of the coating solution and the plating conditions (temperature, current density, etc.).
Such a cell is described, for example, in document EP-A-195.781 (ROBBINS & CRAIG) wherein a band of vertically oriented connectors circulates horizontally and rubs against a belt of flexible, porous material, for example a foam of synthetic resin, in particular of polyurethane; said belt itself circulating in such a manner that the active galvanic solution that impregnates it is continually replaced.
In an embodiment such as the one described above, it is difficult to limit the plating area to a mid-portion of the connectors. Consequently, other embodiments have been proposed, in particular the use of a plating head comprising an elongated prismatic block inserted into a sleeve of porous material impregnated with electrolyte solution. The pieces to be plated are placed longitudinally in contact with an edge of the prismatic block, the angle of the latter determining the width of the portion of porous sheet in contact with the pieces and, thus, the extent of the plated area of said pieces. An illustration of such an embodiment may be found in FIGS. 9, 10 and 11 of reference document EP-A 222 232.